tty: Replace ldisc locking with ldisc_sem (36697529) · Commits · 戴 / test

drivers/tty/tty_buffer.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -429,7 +429,7 @@ static void flush_to_ldisc(struct work_struct *work)
		return;

		disc = tty_ldisc_ref(tty);
		if (disc == NULL) /* !TTY_LDISC */
		if (disc == NULL)
		return;

		spin_lock_irqsave(&buf->lock, flags);

drivers/tty/tty_io.c

+3 −4

Original line number	Diff line number	Diff line
		@@ -1388,8 +1388,7 @@ static int tty_reopen(struct tty_struct *tty)
		struct tty_driver *driver = tty->driver;

		if (test_bit(TTY_CLOSING, &tty->flags) \|\|
		test_bit(TTY_HUPPING, &tty->flags) \|\|
		test_bit(TTY_LDISC_CHANGING, &tty->flags))
		test_bit(TTY_HUPPING, &tty->flags))
		return -EIO;

		if (driver->type == TTY_DRIVER_TYPE_PTY &&
		@@ -1405,7 +1404,7 @@ static int tty_reopen(struct tty_struct *tty)
		}
		tty->count++;

		WARN_ON(!test_bit(TTY_LDISC, &tty->flags));
		WARN_ON(!tty->ldisc);

		return 0;
		}
		@@ -3017,7 +3016,7 @@ void initialize_tty_struct(struct tty_struct *tty,
		tty->pgrp = NULL;
		mutex_init(&tty->legacy_mutex);
		mutex_init(&tty->termios_mutex);
		mutex_init(&tty->ldisc_mutex);
		init_ldsem(&tty->ldisc_sem);
		init_waitqueue_head(&tty->write_wait);
		init_waitqueue_head(&tty->read_wait);
		INIT_WORK(&tty->hangup_work, do_tty_hangup);

drivers/tty/tty_ldisc.c

+46 −283

Original line number	Diff line number	Diff line
		@@ -45,7 +45,6 @@ enum {
		*/

		static DEFINE_RAW_SPINLOCK(tty_ldiscs_lock);
		static DECLARE_WAIT_QUEUE_HEAD(tty_ldisc_wait);
		/* Line disc dispatch table */
		static struct tty_ldisc_ops *tty_ldiscs[NR_LDISCS];

		@@ -153,7 +152,7 @@ static void put_ldops(struct tty_ldisc_ops *ldops)
		* takes tty_ldiscs_lock to guard against ldisc races
		*/

		static struct tty_ldisc *tty_ldisc_get(int disc)
		static struct tty_ldisc tty_ldisc_get(struct tty_struct tty, int disc)
		{
		struct tty_ldisc *ld;
		struct tty_ldisc_ops *ldops;
		@@ -180,8 +179,7 @@ static struct tty_ldisc *tty_ldisc_get(int disc)
		}

		ld->ops = ldops;
		atomic_set(&ld->users, 1);
		init_waitqueue_head(&ld->wq_idle);
		ld->tty = tty;

		return ld;
		}
		@@ -193,20 +191,11 @@ static struct tty_ldisc *tty_ldisc_get(int disc)
		*/
		static inline void tty_ldisc_put(struct tty_ldisc *ld)
		{
		unsigned long flags;

		if (WARN_ON_ONCE(!ld))
		return;

		raw_spin_lock_irqsave(&tty_ldiscs_lock, flags);

		/* unreleased reader reference(s) will cause this WARN */
		WARN_ON(!atomic_dec_and_test(&ld->users));

		ld->ops->refcount--;
		module_put(ld->ops->owner);
		put_ldops(ld->ops);
		kfree(ld);
		raw_spin_unlock_irqrestore(&tty_ldiscs_lock, flags);
		}

		static void tty_ldiscs_seq_start(struct seq_file m, loff_t *pos)
		@@ -257,34 +246,6 @@ const struct file_operations tty_ldiscs_proc_fops = {
		.release = seq_release,
		};

		/**
		* tty_ldisc_try - internal helper
		* @tty: the tty
		*
		* Make a single attempt to grab and bump the refcount on
		* the tty ldisc. Return 0 on failure or 1 on success. This is
		* used to implement both the waiting and non waiting versions
		* of tty_ldisc_ref
		*
		* Locking: takes tty_ldiscs_lock
		*/

		static struct tty_ldisc tty_ldisc_try(struct tty_struct tty)
		{
		unsigned long flags;
		struct tty_ldisc *ld;

		/* FIXME: this allows reference acquire after TTY_LDISC is cleared */
		raw_spin_lock_irqsave(&tty_ldiscs_lock, flags);
		ld = NULL;
		if (test_bit(TTY_LDISC, &tty->flags) && tty->ldisc) {
		ld = tty->ldisc;
		atomic_inc(&ld->users);
		}
		raw_spin_unlock_irqrestore(&tty_ldiscs_lock, flags);
		return ld;
		}

		/**
		* tty_ldisc_ref_wait - wait for the tty ldisc
		* @tty: tty device
		@@ -298,16 +259,15 @@ static struct tty_ldisc tty_ldisc_try(struct tty_struct tty)
		* against a discipline change, such as an existing ldisc reference
		* (which we check for)
		*
		* Locking: call functions take tty_ldiscs_lock
		* Note: only callable from a file_operations routine (which
		* guarantees tty->ldisc != NULL when the lock is acquired).
		*/

		struct tty_ldisc tty_ldisc_ref_wait(struct tty_struct tty)
		{
		struct tty_ldisc *ld;

		/* wait_event is a macro */
		wait_event(tty_ldisc_wait, (ld = tty_ldisc_try(tty)) != NULL);
		return ld;
		ldsem_down_read(&tty->ldisc_sem, MAX_SCHEDULE_TIMEOUT);
		WARN_ON(!tty->ldisc);
		return tty->ldisc;
		}
		EXPORT_SYMBOL_GPL(tty_ldisc_ref_wait);

		@@ -318,13 +278,18 @@ EXPORT_SYMBOL_GPL(tty_ldisc_ref_wait);
		* Dereference the line discipline for the terminal and take a
		* reference to it. If the line discipline is in flux then
		* return NULL. Can be called from IRQ and timer functions.
		*
		* Locking: called functions take tty_ldiscs_lock
		*/

		struct tty_ldisc tty_ldisc_ref(struct tty_struct tty)
		{
		return tty_ldisc_try(tty);
		struct tty_ldisc *ld = NULL;

		if (ldsem_down_read_trylock(&tty->ldisc_sem)) {
		ld = tty->ldisc;
		if (!ld)
		ldsem_up_read(&tty->ldisc_sem);
		}
		return ld;
		}
		EXPORT_SYMBOL_GPL(tty_ldisc_ref);

		@@ -334,27 +299,11 @@ EXPORT_SYMBOL_GPL(tty_ldisc_ref);
		*
		* Undoes the effect of tty_ldisc_ref or tty_ldisc_ref_wait. May
		* be called in IRQ context.
		*
		* Locking: takes tty_ldiscs_lock
		*/

		void tty_ldisc_deref(struct tty_ldisc *ld)
		{
		unsigned long flags;

		if (WARN_ON_ONCE(!ld))
		return;

		raw_spin_lock_irqsave(&tty_ldiscs_lock, flags);
		/*
		* WARNs if one-too-many reader references were released
		* - the last reference must be released with tty_ldisc_put
		*/
		WARN_ON(atomic_dec_and_test(&ld->users));
		raw_spin_unlock_irqrestore(&tty_ldiscs_lock, flags);

		if (waitqueue_active(&ld->wq_idle))
		wake_up(&ld->wq_idle);
		ldsem_up_read(&ld->tty->ldisc_sem);
		}
		EXPORT_SYMBOL_GPL(tty_ldisc_deref);

		@@ -437,27 +386,6 @@ static void __lockfunc tty_ldisc_enable_pair(struct tty_struct *tty,
		tty_ldisc_unlock_pair(tty, tty2);
		}


		/**
		* tty_ldisc_enable - allow ldisc use
		* @tty: terminal to activate ldisc on
		*
		* Set the TTY_LDISC flag when the line discipline can be called
		* again. Do necessary wakeups for existing sleepers. Clear the LDISC
		* changing flag to indicate any ldisc change is now over.
		*
		* Note: nobody should set the TTY_LDISC bit except via this function.
		* Clearing directly is allowed.
		*/

		static void tty_ldisc_enable(struct tty_struct *tty)
		{
		clear_bit(TTY_LDISC_HALTED, &tty->flags);
		set_bit(TTY_LDISC, &tty->flags);
		clear_bit(TTY_LDISC_CHANGING, &tty->flags);
		wake_up(&tty_ldisc_wait);
		}

		/**
		* tty_ldisc_flush - flush line discipline queue
		* @tty: tty
		@@ -555,14 +483,14 @@ static void tty_ldisc_restore(struct tty_struct tty, struct tty_ldisc old)
		int r;

		/* There is an outstanding reference here so this is safe */
		old = tty_ldisc_get(old->ops->num);
		old = tty_ldisc_get(tty, old->ops->num);
		WARN_ON(IS_ERR(old));
		tty->ldisc = old;
		tty_set_termios_ldisc(tty, old->ops->num);
		if (tty_ldisc_open(tty, old) < 0) {
		tty_ldisc_put(old);
		/* This driver is always present */
		new_ldisc = tty_ldisc_get(N_TTY);
		new_ldisc = tty_ldisc_get(tty, N_TTY);
		if (IS_ERR(new_ldisc))
		panic("n_tty: get");
		tty->ldisc = new_ldisc;
		@@ -575,101 +503,6 @@ static void tty_ldisc_restore(struct tty_struct tty, struct tty_ldisc old)
		}
		}

		/**
		* tty_ldisc_wait_idle - wait for the ldisc to become idle
		* @tty: tty to wait for
		* @timeout: for how long to wait at most
		*
		* Wait for the line discipline to become idle. The discipline must
		* have been halted for this to guarantee it remains idle.
		*/
		static int tty_ldisc_wait_idle(struct tty_struct *tty, long timeout)
		{
		long ret;
		ret = wait_event_timeout(tty->ldisc->wq_idle,
		atomic_read(&tty->ldisc->users) == 1, timeout);
		return ret > 0 ? 0 : -EBUSY;
		}

		/**
		* tty_ldisc_halt - shut down the line discipline
		* @tty: tty device
		* @o_tty: paired pty device (can be NULL)
		* @timeout: # of jiffies to wait for ldisc refs to be released
		*
		* Shut down the line discipline and work queue for this tty device and
		* its paired pty (if exists). Clearing the TTY_LDISC flag ensures
		* no further references can be obtained, while waiting for existing
		* references to be released ensures no more data is fed to the ldisc.
		*
		* You need to do a 'flush_scheduled_work()' (outside the ldisc_mutex)
		* in order to make sure any currently executing ldisc work is also
		* flushed.
		*/

		static int tty_ldisc_halt(struct tty_struct tty, struct tty_struct o_tty,
		long timeout)
		{
		int retval;

		clear_bit(TTY_LDISC, &tty->flags);
		if (o_tty)
		clear_bit(TTY_LDISC, &o_tty->flags);

		retval = tty_ldisc_wait_idle(tty, timeout);
		if (!retval && o_tty)
		retval = tty_ldisc_wait_idle(o_tty, timeout);
		if (retval)
		return retval;

		set_bit(TTY_LDISC_HALTED, &tty->flags);
		if (o_tty)
		set_bit(TTY_LDISC_HALTED, &o_tty->flags);

		return 0;
		}

		/**
		* tty_ldisc_hangup_halt - halt the line discipline for hangup
		* @tty: tty being hung up
		*
		* Shut down the line discipline and work queue for the tty device
		* being hungup. Clear the TTY_LDISC flag to ensure no further
		* references can be obtained and wait for remaining references to be
		* released to ensure no more data is fed to this ldisc.
		* Caller must hold legacy and ->ldisc_mutex.
		*
		* NB: tty_set_ldisc() is prevented from changing the ldisc concurrently
		* with this function by checking the TTY_HUPPING flag.
		*/
		static bool tty_ldisc_hangup_halt(struct tty_struct *tty)
		{
		char cur_n[TASK_COMM_LEN], tty_n[64];
		long timeout = 3 * HZ;

		clear_bit(TTY_LDISC, &tty->flags);

		if (tty->ldisc) { /* Not yet closed */
		tty_unlock(tty);

		while (tty_ldisc_wait_idle(tty, timeout) == -EBUSY) {
		timeout = MAX_SCHEDULE_TIMEOUT;
		printk_ratelimited(KERN_WARNING
		"%s: waiting (%s) for %s took too long, but we keep waiting...\n",
		__func__, get_task_comm(cur_n, current),
		tty_name(tty, tty_n));
		}

		set_bit(TTY_LDISC_HALTED, &tty->flags);

		/* must reacquire both locks and preserve lock order */
		mutex_unlock(&tty->ldisc_mutex);
		tty_lock(tty);
		mutex_lock(&tty->ldisc_mutex);
		}
		return !!tty->ldisc;
		}

		/**
		* tty_set_ldisc - set line discipline
		* @tty: the terminal to set
		@@ -679,103 +512,47 @@ static bool tty_ldisc_hangup_halt(struct tty_struct *tty)
		* context. The ldisc change logic has to protect itself against any
		* overlapping ldisc change (including on the other end of pty pairs),
		* the close of one side of a tty/pty pair, and eventually hangup.
		*
		* Locking: takes tty_ldiscs_lock, termios_mutex
		*/

		int tty_set_ldisc(struct tty_struct *tty, int ldisc)
		{
		int retval;
		struct tty_ldisc o_ldisc, new_ldisc;
		struct tty_struct *o_tty;
		struct tty_struct *o_tty = tty->link;

		new_ldisc = tty_ldisc_get(ldisc);
		new_ldisc = tty_ldisc_get(tty, ldisc);
		if (IS_ERR(new_ldisc))
		return PTR_ERR(new_ldisc);

		tty_lock(tty);
		/*
		* We need to look at the tty locking here for pty/tty pairs
		* when both sides try to change in parallel.
		*/

		o_tty = tty->link; /* o_tty is the pty side or NULL */

		retval = tty_ldisc_lock_pair_timeout(tty, o_tty, 5 * HZ);
		if (retval) {
		tty_ldisc_put(new_ldisc);
		return retval;
		}

		/*
		* Check the no-op case
		*/

		if (tty->ldisc->ops->num == ldisc) {
		tty_unlock(tty);
		tty_ldisc_enable_pair(tty, o_tty);
		tty_ldisc_put(new_ldisc);
		return 0;
		}

		mutex_lock(&tty->ldisc_mutex);

		/*
		* We could be midstream of another ldisc change which has
		* dropped the lock during processing. If so we need to wait.
		*/

		while (test_bit(TTY_LDISC_CHANGING, &tty->flags)) {
		mutex_unlock(&tty->ldisc_mutex);
		tty_unlock(tty);
		wait_event(tty_ldisc_wait,
		test_bit(TTY_LDISC_CHANGING, &tty->flags) == 0);
		tty_lock(tty);
		mutex_lock(&tty->ldisc_mutex);
		}

		set_bit(TTY_LDISC_CHANGING, &tty->flags);

		/*
		* No more input please, we are switching. The new ldisc
		* will update this value in the ldisc open function
		*/

		/* FIXME: why 'shutoff' input if the ldisc is locked? */
		tty->receive_room = 0;

		o_ldisc = tty->ldisc;

		tty_unlock(tty);
		/*
		* Make sure we don't change while someone holds a
		* reference to the line discipline. The TTY_LDISC bit
		* prevents anyone taking a reference once it is clear.
		* We need the lock to avoid racing reference takers.
		*
		* We must clear the TTY_LDISC bit here to avoid a livelock
		* with a userspace app continually trying to use the tty in
		* parallel to the change and re-referencing the tty.
		*/

		retval = tty_ldisc_halt(tty, o_tty, 5 * HZ);

		/*
		* Wait for hangup to complete, if pending.
		* We must drop the mutex here in case a hangup is also in process.
		*/

		mutex_unlock(&tty->ldisc_mutex);

		flush_work(&tty->hangup_work);

		tty_lock(tty);
		mutex_lock(&tty->ldisc_mutex);

		/* handle wait idle failure locked */
		if (retval) {
		tty_ldisc_put(new_ldisc);
		goto enable;
		}
		/* FIXME: for testing only */
		WARN_ON(test_bit(TTY_HUPPED, &tty->flags));

		if (test_bit(TTY_HUPPING, &tty->flags)) {
		/* We were raced by the hangup method. It will have stomped
		the ldisc data and closed the ldisc down */
		clear_bit(TTY_LDISC_CHANGING, &tty->flags);
		mutex_unlock(&tty->ldisc_mutex);
		tty_ldisc_enable_pair(tty, o_tty);
		tty_ldisc_put(new_ldisc);
		tty_unlock(tty);
		return -EIO;
		@@ -804,14 +581,10 @@ int tty_set_ldisc(struct tty_struct *tty, int ldisc)

		tty_ldisc_put(o_ldisc);

		enable:
		/*
		* Allow ldisc referencing to occur again
		*/

		tty_ldisc_enable(tty);
		if (o_tty)
		tty_ldisc_enable(o_tty);
		tty_ldisc_enable_pair(tty, o_tty);

		/* Restart the work queue in case no characters kick it off. Safe if
		already running */
		@@ -819,7 +592,6 @@ enable:
		if (o_tty)
		schedule_work(&o_tty->port->buf.work);

		mutex_unlock(&tty->ldisc_mutex);
		tty_unlock(tty);
		return retval;
		}
		@@ -852,7 +624,7 @@ static void tty_reset_termios(struct tty_struct *tty)

		static int tty_ldisc_reinit(struct tty_struct *tty, int ldisc)
		{
		struct tty_ldisc *ld = tty_ldisc_get(ldisc);
		struct tty_ldisc *ld = tty_ldisc_get(tty, ldisc);

		if (IS_ERR(ld))
		return -1;
		@@ -891,14 +663,8 @@ void tty_ldisc_hangup(struct tty_struct *tty)

		tty_ldisc_debug(tty, "closing ldisc: %p\n", tty->ldisc);

		/*
		* FIXME! What are the locking issues here? This may me overdoing
		* things... This question is especially important now that we've
		* removed the irqlock.
		*/
		ld = tty_ldisc_ref(tty);
		if (ld != NULL) {
		/* We may have no line discipline at this point */
		if (ld->ops->flush_buffer)
		ld->ops->flush_buffer(tty);
		tty_driver_flush_buffer(tty);
		@@ -909,21 +675,22 @@ void tty_ldisc_hangup(struct tty_struct *tty)
		ld->ops->hangup(tty);
		tty_ldisc_deref(ld);
		}
		/*
		* FIXME: Once we trust the LDISC code better we can wait here for
		* ldisc completion and fix the driver call race
		*/

		wake_up_interruptible_poll(&tty->write_wait, POLLOUT);
		wake_up_interruptible_poll(&tty->read_wait, POLLIN);

		tty_unlock(tty);

		/*
		* Shutdown the current line discipline, and reset it to
		* N_TTY if need be.
		*
		* Avoid racing set_ldisc or tty_ldisc_release
		*/
		mutex_lock(&tty->ldisc_mutex);
		tty_ldisc_lock_pair(tty, tty->link);
		tty_lock(tty);

		if (tty_ldisc_hangup_halt(tty)) {
		if (tty->ldisc) {

		/* At this point we have a halted ldisc; we want to close it and
		reopen a new ldisc. We could defer the reopen to the next
		@@ -942,9 +709,8 @@ void tty_ldisc_hangup(struct tty_struct *tty)
		BUG_ON(tty_ldisc_reinit(tty, N_TTY));
		WARN_ON(tty_ldisc_open(tty, tty->ldisc));
		}
		tty_ldisc_enable(tty);
		}
		mutex_unlock(&tty->ldisc_mutex);
		tty_ldisc_enable_pair(tty, tty->link);
		if (reset)
		tty_reset_termios(tty);

		@@ -976,15 +742,12 @@ int tty_ldisc_setup(struct tty_struct tty, struct tty_struct o_tty)
		tty_ldisc_close(tty, ld);
		return retval;
		}
		tty_ldisc_enable(o_tty);
		}
		tty_ldisc_enable(tty);
		return 0;
		}

		static void tty_ldisc_kill(struct tty_struct *tty)
		{
		mutex_lock(&tty->ldisc_mutex);
		/*
		* Now kill off the ldisc
		*/
		@@ -995,7 +758,6 @@ static void tty_ldisc_kill(struct tty_struct *tty)

		/* Ensure the next open requests the N_TTY ldisc */
		tty_set_termios_ldisc(tty, N_TTY);
		mutex_unlock(&tty->ldisc_mutex);
		}

		/**
		@@ -1017,15 +779,16 @@ void tty_ldisc_release(struct tty_struct tty, struct tty_struct o_tty)

		tty_ldisc_debug(tty, "closing ldisc: %p\n", tty->ldisc);

		tty_ldisc_halt(tty, o_tty, MAX_SCHEDULE_TIMEOUT);

		tty_ldisc_lock_pair(tty, o_tty);
		tty_lock_pair(tty, o_tty);
		/* This will need doing differently if we need to lock */

		tty_ldisc_kill(tty);
		if (o_tty)
		tty_ldisc_kill(o_tty);

		tty_unlock_pair(tty, o_tty);
		tty_ldisc_unlock_pair(tty, o_tty);

		/* And the memory resources remaining (buffers, termios) will be
		disposed of when the kref hits zero */

		@@ -1042,7 +805,7 @@ void tty_ldisc_release(struct tty_struct tty, struct tty_struct o_tty)

		void tty_ldisc_init(struct tty_struct *tty)
		{
		struct tty_ldisc *ld = tty_ldisc_get(N_TTY);
		struct tty_ldisc *ld = tty_ldisc_get(tty, N_TTY);
		if (IS_ERR(ld))
		panic("n_tty: init_tty");
		tty->ldisc = ld;

include/linux/tty.h

+1 −3

Original line number	Diff line number	Diff line
		@@ -238,7 +238,7 @@ struct tty_struct {
		int index;

		/* Protects ldisc changes: Lock tty not pty */
		struct mutex ldisc_mutex;
		struct ld_semaphore ldisc_sem;
		struct tty_ldisc *ldisc;

		struct mutex atomic_write_lock;
		@@ -305,8 +305,6 @@ struct tty_file_private {
		#define TTY_DO_WRITE_WAKEUP 5 /* Call write_wakeup after queuing new */
		#define TTY_PUSH 6 /* n_tty private */
		#define TTY_CLOSING 7 /* ->close() in progress */
		#define TTY_LDISC 9 /* Line discipline attached */
		#define TTY_LDISC_CHANGING 10 /* Line discipline changing */
		#define TTY_LDISC_OPEN 11 /* Line discipline is open */
		#define TTY_PTY_LOCK 16 /* pty private */
		#define TTY_NO_WRITE_SPLIT 17 /* Preserve write boundaries to driver */

include/linux/tty_ldisc.h

+1 −2

Original line number	Diff line number	Diff line
		@@ -203,8 +203,7 @@ struct tty_ldisc_ops {

		struct tty_ldisc {
		struct tty_ldisc_ops *ops;
		atomic_t users;
		wait_queue_head_t wq_idle;
		struct tty_struct *tty;
		};

		#define TTY_LDISC_MAGIC 0x5403

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